1. Field of the Invention
The present invention relates to a magnetic disk drive used in, for example, an external storage device of a computer.
2. Description of the Related Art
A conventional magnetic disk drive is described. FIG. 14 is a plan view schematically showing the conventional magnetic disk drive. FIG. 15 is a right side view of the main portion as viewed in the direction of arrow XIV in FIG. 14, in which a chassis and a bottom cover in the conventional magnetic disk drive are in an assembled state. FIG. 16 is a plan view of the bottom cover in the conventional magnetic disk drive. FIG. 17 shows measured values obtained when a body of the conventional magnetic disk drive is resonating.
In FIGS. 14 to 16, a chassis 31 is a thin iron plate, and comprises a flat section 31a which is a substantially rectangular flat surface, side walls 31b1 and 31b2 formed vertically from both longer sides of the flat section 31a, and a side wall 31c formed by erecting vertically a portion of one of the shorter sides of the flat section 31a. Near a boundary between the flat section 31a and the side wall 31b l, recess-shaped holding sections 32 which are recessed from the flat section 31a are formed at two locations in a longitudinal direction of the chassis 31. Similarly, near a boundary between the side wall 31b 2 and the flat section 31a, recess-shaped holding sections 32 are formed at two locations in the longitudinal direction of the chassis 31. The sets of two holding sections 32 near the two boundaries of the chassis 31 are disposed parallel to each other with 1respect to a center line X3xe2x80x94X3 extending in the longitudinal direction of the chassis 31.
Each holding section 32 includes a tapering section 32a and a pedestal 32b which is a top portion formed continuously with its corresponding tapering section 32a and formed parallel to the flat surface corresponding to the flat section 31a, with a through hole 32c passing vertically through substantially the center of its corresponding pedestal 32b. 
A head transporting device 33 comprises a head carriage 34 including a head arm for carrying a magnetic head (not shown) at an end thereof, a guide shaft 35 which is inserted into the head carriage 34, and a stepping motor 36 to which one end of the guide shaft 35 is fitted. The stepping motor 36 allows the head carriage 34 to move in the longitudinal direction of the chassis 31. The head transporting device 33 which is inserted into a hole (not shown) formed in the side wall 31c is secured to the chassis 31 using a desired securing means such as screwing.
A spindle motor 37 is mounted to the flat section 31a of the chassis 31 from below using a desired mounting means such as screwing. Although not shown, other component parts are mounted to the chassis 31 to form a body A1.
As shown in FIG. 16, a bottom cover 38 is a thin iron plate, and comprises a bottom plate 38a which is a substantially rectangular flat surface, and side walls 38b1 and 38b2 formed vertically from both longer sides of the bottom plate 38a. Near a boundary between the bottom plate 38a and the side wall 38b1, protruding holding sections 39 formed by indenting portions of the bottom plate 38a from the bottom side to the top side are formed at two locations in a longitudinal direction of the bottom cover 38. Similarly, near a boundary between the side wall 38b2 and the bottom plate 38a, protruding holding sections 39 are formed at two locations in the longitudinal direction. The sets of two holding sections near the two boundaries of the bottom plate 38a are disposed parallel to each other with respect to a center line X4xe2x80x94X4 extending in the longitudinal direction.
Similarly to each holding section 32 of the chassis 31, each holding section 39 includes a tapering section 39a and a pedestal 39b which is a top portion formed continuously with its corresponding tapering section 39a and formed parallel to the flat surface of the bottom plate 38a, with a hole 39c passing vertically through substantially the center of its corresponding pedestal 39b. 
As shown in FIG. 15, the bottom cover 38 is mounted to the chassis 31 so as to cover the bottom side of the chassis 31 and so as to make the pedestal 32b of each holding section 32 of the chassis 31 contact, that is, abut against the pedestal 39b of each holding section 39 of the bottom cover 38. This causes the hole 39c in each holding section 39 of the bottom cover 38 and the hole 32c of each holding section 32 of the chassis 31 to be in a connected state. Holding means, such as screws 40, are inserted into the holes 39c and the corresponding holes 32c in the connected state in order to secure the bottom cover 38 and the chassis 31 together. Accordingly, the bottom cover 38 is completely secured to the chassis 31 at four locations with the screws. By mounting the bottom cover 38 to the body A1, the magnetic disk drive is constructed.
The magnetic disk drive is used as an external storage device of a computer, such as a desktop PC, and is placed in various external environmental conditions. It functions to perform read/write operations with a magnetic head which sandwiches a magnetic floppy disk from both sides thereof.
Therefore, when the magnetic disk drive is vibrated by changes in some external environmental condition, the vibration acts on the magnetic head through the head carriage, so that the read/write operations may be affected in some way.
Here, as shown in FIG. 17, an evaluation of the vibration of the body A1 was carried out by vibrating the entire conventional magnetic disk drive and changing the oscillation frequency thereof using a measuring device called a servo analyzer. In FIG. 17, the vertical axis represents a ratio in which an output acceleration a1 of the body A1 is divided by an input acceleration a2 to the magnetic disk drive (a1/a2), and the horizontal axis represents the oscillation frequency (in Hz).
According to FIG. 17, at input frequencies of 230 Hz and 317 Hz, the a1/a2 level become steep and reach peak points. From FIG. 17, it can be seen that the body A1 resonates when the outside vibration has vibration frequencies of 230 Hz and 317 Hz.
As can be understood from the foregoing description, in the conventional magnetic disk drive, the chassis 31 and the bottom cover 38 are completely secured together by the four holding sections 32 of the chassis 31 and the four holding sections 39 of the bottom cover 38, so that any vibration and shock exerted to the bottom cover 38 from the outside are directly transmitted to the body A1. Therefore, as shown in FIG. 17, resonance occurs at 200 to 350 Hz. When the body A1 resonates, the spindle motor 37, the head carriage 34, and the like are adversely affected, so that, for example, variations in rotation occur therein. In particular, the head carriage 34 itself has a natural resonance mode near 300 Hz, so that the head carriage 34 is greatly affected, causing a side of the head arm where the magnetic disk is gripped to open, resulting in read/write operation errors.
Accordingly, it is an object of the present invention to make it possible to effectively reduce externally applied vibration and shock by making a body comprising a chassis to which component parts are mounted rotatable with reference to a location situated away from the center of gravity of the body.
To this end, according to the present invention, there is provided a magnetic disk drive comprising:
a body including a chassis formed of a flat plate and at least a spindle motor and a head carriage that are mounted to the chassis;
a bottom cover mounted so as to cover the chassis; and
holding means for holding the chassis and the bottom cover;
wherein the holding means is disposed on a support line which intersects at right angles a line passing through the center of gravity of the body and extending in a direction of movement of the head carriage, the support line being displaced from the center of gravity of the body; and
wherein the body is rotatable with respect to the bottom cover, with the support line serving as an axis.
Two such holding means may be provided at two locations on the support line, with the line passing through the center of gravity being disposed therebetween.
The holding means may be symmetrically disposed at the two locations with respect to the line passing through the center of gravity.
The holding means may be disposed on the support line displaced at a spindle motor side.
The magnetic disk drive comprising the holding means may further comprise a resilient member for absorbing shock at the chassis, wherein, at a location displaced from the support line, the resilient member is disposed between the chassis and the bottom cover.
The magnetic disk drive comprising the holding means may further comprise a resilient member for absorbing shock produced at the chassis, wherein, at a location displaced from the support line, the resilient member is disposed at a head carriage mounting side between the chassis and the bottom cover.
The magnetic disk drive comprising the holding means may be such that the resilient member performs an urging operation in a direction in which the bottom cover and the chassis are separated from each other or in a direction in which the bottom cover and the chassis are brought toward each other.
The magnetic disk drive comprising the holding means may further comprise restricting means for restricting a rotational movement of the chassis, with the holding means serving as a fulcrum.
The magnetic disk drive comprising the holding means may be such that the restricting means comprises a hole formed in either one of the bottom cover and the chassis and a protrusion formed in either of the other of the bottom cover and the chassis.
The magnetic disk drive comprising the holding means may be such that, in the direction of movement of the head carriage, the chassis while being tilted with respect to the bottom cover, is held by the holding means, and the tilted chassis while being displaced is stopped by the restricting means for restricting a rotational motion of the chassis with the holding means as a fulcrum.
The magnetic disk drive comprising the holding means may be such that either the chassis or the bottom cover includes a first pedestal having an inclined surface formed at a top portion thereof; the holding means is situated at the first pedestal; and either the chassis or the bottom cover is brought into contact with the inclined surface in order to dispose the chassis in a tilted state with respect to the bottom cover.
The magnetic disk drive comprising the holding means may be such that two such first pedestals are provided at two locations on the support line, with the line passing through the center of gravity being disposed therebetween
The magnetic disk drive comprising the holding means may be such that either the chassis or the bottom cover includes a second pedestal having a top surface which is parallel to a flat surface of either the chassis or the bottom cover; the holding means is situated at the second pedestal; on the support line, the second pedestal is disposed on one side of the line passing through the center of gravity, and the first pedestal is disposed on the other side of the line passing through the center of gravity; either the chassis or the bottom cover is brought into contact with the inclined surface and the top surface in order to hold the chassis and the bottom cover by the holding means; and the magnetic disk drive further comprises a resilient member for absorbing shock at the chassis, in which, at a location separated from the second pedestal between the chassis and the bottom cover, the resilient member is disposed towards the second pedestal from the line passing through the center of gravity.